I'll admit... this is one of the only modules where I had trouble understanding the manual.

1. Look at the first digit in the slot.
2. Apply the first rule from the 'all slots' section. (If it's a 2, replace it with a 5. If it's a 7, replace it with a zero)
3. Continue with the number you get after that rule, and apply rule 2 from the 'all slots' section (For every lit indicator add 1 to the number and subtract 1 for every unlit indicator.)
4. Apply only ONE of the remaining 5 rules in this section! Take THAT number to step 5.

Extra:
"Otherwise, if there is an RCA or a PS/2 port on the bomb, skip the rest of the rules in this section." - If this rule applies: continue to the section '1st slot' with the number you calculated AFTER step 2

"Otherwise, take the original digit and add the number of batteries on the bomb." - If this rule applies (which means neither of the other 4 didn't) Forget every rule you applied! Take the initial first digit in the slot and add the number of bateries. Continue to the '1st slot' section with this number.

5. Go to the '1st slot' section with the number you calculated after step 4.
6. Apply only ONE of the rules in this section!
7. If the final number you calculated is below 0, add 10 till the number is 0-9. If it's above 9, substract 10 till the number is 0-9/

7. Repeat step 1-7 for the 2nd and the 3rd digit. (but don't forget to look at the '2nd slot' section for the 2nd digit and the '3rd slot' section for the 3rd digit.

Still can't get this to work... The rules under the "All Slots" section should be applied to every digit of the number or...?
For example, if the number was 726 i should transform it in 056;
Let's say the bomb has 2 lit indicators : the number should now be 058 or 278?
If the number is a multiple of 3 add 4 to it... Which number??? Every digit or the entire number???

The rules under the all slots section apply to each digit individually. So you take the first digit and run through the rules in the all slots section and then repeat that with the other two digits.